1. Field of the Invention
This invention relates to pneumatic radial tires. More particularly it relates to a method of producing pneumatic radial tires which can advantageously improve high-speed running performances of the tire and a bladder used therefor.
2. Disclosure of the Related Art
A pneumatic radial tire comprises a carcass comprised of at least one cord ply of radial arrangement and a belt superimposed about a crown portion of the carcass and comprised of plural cord layers. This construction has many advantages in that the motion of tread rubber constituting the tread portion of the tire is reduced by a so-called "hoop" effect of the belt as compared with that of bias tires. Also, the durability, wear resistance and steering stability are excellent and the rolling resistance is low and the like. Therefore, these radial tires are favorably mounted onto many vehicles and used with recent enlargement of development of expressway networks.
On the other hand, the reinforcement is added to tread portion and bead portion of the pneumatic radial tire to cope with the high-speed running accompanied with recent improvement of vehicle performances, but it is strongly demanded to more improve the high-speed running performances of the tire in accordance with improvement of vehicle performances.
Therefore, there are proposed various techniques such as a change of end count and cord angle in the cords constituting the carcass or the belt, addition of a new reinforcing member and the like for controlling strain or heat generation at portions easily causing troubles or enhancing the rigidity of the tire casing.
In these proposed techniques, the rigidity of the tire casing as a whole is increased to create portions having undesirably increased rigidity, which is unfavorable in the running performances of tire and the ride comfortability. Also, there are caused inconveniences such as rise of cost, increase of weight and the like accompanied with the increase of the reinforcing members.